An air bag device that protects an occupant of a vehicle by deploying an air bag at the time of collision of the vehicle, for example, is known to be an example of an occupant protection device. When an impact applied to a vehicle is measured by G sensors disposed at each section of the vehicle, the air bag device converts the measured values obtained as a result thereof into digital signals and transmits those signals to an air bag electronic control unit (ECU); thus, the air bag ECU determines the presence or absence of a collision based on the received impact acceleration and controls actuation of front air bags and side air bag on the basis of that determination.
Consequently, it is important to distinguish between vibration components and collision components in terms of determining the need to actuate an air bag installed in a vehicle. For example, among components of a frontal collision, it is not necessary to actuate an occupant protection device in response to vibration components generated when traveling over rough roads, while among components of a side collision, since vibration components not requiring actuation of the occupant protection device may be generated when a vehicle door is shut with an excessive force, it is desirable to eliminate these components by an arithmetic operation. Similarly, with respect to rollovers as well, since an unnecessary angular velocity component is also generated when traveling over rough roads, it is necessary to distinguish between vibration components and collision components attributable to a rollover. Thus, it is necessary that activation of the occupant protection device be determined rapidly within several tens of milliseconds from the start of a collision but without causing an erroneous operation in response to unnecessary components.
In order to satisfy the above requirements, the following method has been conventionally employed: when G sensors are installed in a vehicle, acceleration components detected by the G sensors are integrated, and the occupant protection device is activated in the case the integral value exceeds a fixed value. In addition, a system has also been proposed that activates an occupant protection device by assessing a collision using multiple infinite impulse response (IIR) type linear filters (see, for example, Patent Document 1).
Patent Document 1: JP-A-04-146847
According to the conventional technology as described above, in the case of providing a low pass filter (LPF) for removing high-frequency components, it is necessary to lower the cutoff frequency of the LPF or set a higher order in order to attenuate vibration components. On the other hand, in order to prevent collision components from being delayed, it is necessary to raise the cutoff frequency of the LPF or set a lower order. Thus, there is a need to satisfy the aforementioned offsetting parameters.
In addition, according to the technology disclosed in Patent Document 1, although it is possible to shorten the time required for determination according to the assessment method used to carry out integration, and thus control air bag deployment at the proper timing, in the case vibration components and collision components are at the same input level, there is no difference in output values, thus making it difficult to accurately distinguish between vibration components and collision components.